This is a randomized, controlled, double-blinded, three armed, 5 year trial of angiotensin converting enzyme inhibition (Enalapril), angiotensin II receptor blockade (Losartan), and placebo in prevention of the early renal structural changes of diabetes measured by morphometry in normoalbuminuric, normotensive, IDDM patients with normal glomerular filtration rate (GFR). The aim is to recruit 285 patients in three centers (U of Minnesota, McGill University and the University of Toronto) and to compare the three groups for the primary endpoint of the rate of mesangial expansion as measured in two renal biopsies performed five years apart. Interval measures will include urinary albumin excretion, GFR and glycemia.